prototype(#53): palette candidates as runtime token swaps

Throwaway. Tokenises the theme's literal colours so candidate palettes can be
swapped in the browser, adds three candidates (Plum Noir one-metal, two-metal
pewter, two-metal plus a champagne inset), a WCAG checker, a seeder and the
screenshots they are judged on.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

prototype/candidate-c.css

@@ -0,0 +1,17 @@
+/* C — Two Metals + plain paper. B + one champagne inset, to test whether a light surface earns a slot. */
+:root {
+  --wg-paper: #EFE5D2;
+  --wg-ink-on-light: #351E28;
+  --wg-focus-ring-on-light: #09080B;
+}
+/* the inset: quoted material is paper pasted into the ledger. No metal on it (#50 finding 9). */
+blockquote, .wg-paper {
+  background: var(--wg-paper) !important;
+  color: var(--wg-ink-on-light) !important;
+  border: 0 !important;
+  border-left: 3px solid var(--wg-red) !important;
+  box-shadow: 0 1px 0 rgba(0,0,0,.5), 0 10px 22px rgba(0,0,0,.35) !important;
+}
+blockquote a, .wg-paper a { color: #6E1F2A !important; }
+blockquote *, .wg-paper * { color: inherit !important; }
+blockquote :focus-visible, .wg-paper :focus-visible { outline-color: var(--wg-focus-ring-on-light) !important; }